1. Technical Field
The invention relates to an arrangement and a method for operating self-steering wheels on a non-driving axle in a vehicle having a specially designed double-acting cylinder that in a first position allows self-steering of the wheels and in a second position locks the wheels in a position parallel to the longitudinal direction of the vehicle.
2. Background Art
As a rule, vehicles provided with more than one rear axle, for example, trucks with twin rear axles of which only one is driven, have problems maneuvering at low speeds and on tight bends. The maximum permitted axle load on many roads often makes it necessary to distribute the weight of the vehicle over a number of axles. There are also regulations laid down by authorities relating to the distance between the axles. These limitations are in opposition to a desire for a short wheelbase in order to obtain a maneuverable vehicle with a small turning radius.
One solution to this problem is to provide the non-driven wheel axle with wheels that are self-steering under certain circumstances. EP 0845403 A2 discloses a hydraulic system in which the position of the wheels is controlled by the power steering of the vehicle, but which results in a complicated solution that requires long runs of hydraulic lines and also a separate hydraulic system for the self-steering wheel pair. GB 2202811 A2 discloses a system with a pair of individually adjustable pistons and mechanical locking devices, which locks have to be released and locked every time the wheels are to be maneuvered. DE 29 48 181 A1 discloses two separate pistons that each act on their own wheel, the wheels being connected to a parallel tie rod. In the latter solution, the pistons are pressurized for traveling straight ahead and unpressurized when self-steering is desired. As both the pistons are spring-loaded, there is a certain risk of fluctuations in the system while traveling straight ahead, as both the pistons lie between their end positions and can thus move in both directions. The system is also sensitive to variations in the pressure from the pressure source. At high speeds, even small fluctuations can give rise to rapid tire wear. In the self-steering position, the wheels have to overcome the spring force of the two return springs before a wheel deflection can be brought about, a function that can result in the wheels lagging behind with increased friction and tire wear as a consequence.
The present invention aims to produce an arrangement for self-steering which solves the problems mentioned above.